1. Field of the Invention
This invention relates to an orthopedic trial femoral component for use in determining the correct prosthetic femoral component for implantation from a group of prosthetic femoral components. These implants are utilized in replacing the head and neck of a femur with a prosthetic part. More particularly, this invention relates to a two-piece trial component which can be used to guide the surgeon in resecting a damaged femur head and neck and replacing it with a prosthetic femoral component of the proper size.
2. Description of the Prior Art
A surgical operation to replace the femur head and neck with a prosthetic femoral component is a complex operation and requires a relatively long time. There has been a long felt need for methods to simplify and shorten this surgery. This is especially true since many of the patients requiring such surgery are elderly, frail or otherwise sick and cannot withstand long operations. In addition, in the trauma area, most individuals needing a femur head/neck replacement are multitrauma patients who require a series of surgical operations performed by different surgeons.
In all these examples, the longer the patient is under anesthesia, the greater the risk to the health of the patient. In the past as a guide during surgery, surgeons used a series of one-piece trail prostheses, which trail prostheses were identical in size to the corresponding prosthetic implants. Normally, prosthetic femoral component implants come in discrete sizes, which sizes have been determined to cover the widest range of patients surgeons are likely to encounter. Since the human femur varies markedly in size, orthopedic implant manufacturers have provided individual femoral component implants sized to cover a range of different sized individuals. Usually, the surgeon examines X-rays to determine the approximate size femoral prosthesis, from a discrete group of sizes, which would be required. He then uses the corresponding trial component as a guide to prepare the femur to receive the prosthesis chosen.
Often, however, the surgeon finds upon implantation that either his preparation of the femur was incorrect or that the three dimensional body geometry does not allow for the incorporation of the preliminarily chosen femoral component. Manufacturers compensate for these problems by providing femoral prosthesis components with identical stem lengths but different neck/body sizes or vice versa. In the prior art systems the surgeon has a series of one-piece trial components with multiple stem and body sizes. Each one-piece trial component will have a body portion of predetermined size attached to it. The surgeon then uses trial and error selection of trial prostheses to determine the best fitting component.
Since in the past manufacturers have supplied a trial component corresponding to each of a plurality of femoral prostheses, the surgeon must attempt to get a trial stem to fit so that his final component will likewise be correctly sized. This is difficult because the surgeon cannot view the medullary canal fit of a trial stem in a one-piece trial component because the proximal body block his view. Thus the surgeon must ream and/or rasp the femoral canal until, through feel and guess-work, he thinks the trial stem fits. However, especially in cemented applications, it is difficult for the surgeon to see the gap created by his reaming and thus determine the actual gap to be filled by the bone cement.
In a one-piece trial component, when the surgeon puts the trial stem into the bone, the proximal body tries to seat on the free-hand cut made by the surgeon in the femoral neck area at the start of the operation. Normally this cut is a 90.degree. L-shaped cut, removing the head and neck of the natural femur. While working on the fit of the distal stem portion, the surgeon may actually contact a bony obstruction at the proximal end of the femur with the body portion of the trial prosthesis. At this point, it is extremely difficult to discern whether the problem is located distally around the stem or proximally around the body portion of the trial prosthesis. If the problem is in the proximal area of the bone, then the surgeon must re-cut the proximal 9.degree. surface. This process may have to be repeated a number of times to make the trial component fit correctly both in the distal stem area and in the proximal body area.
By use of the present invention, it has been found that the problems with the prior are surgical techniques can be overcome. Specifically, in the present invention, the distal stem and proximal body portions of the femoral component are fitted separately. To this end, the present invention provides a two-piece trial component kit with a plurality of interchangeable heads and stems. With the system of the present invention, the surgeon may either address the distal stem fit or the proximal body fit first. More importantly, the surgeon can address each fit distinctly and independently, i.e., the stem portion separately from the proximal body portion.
In the preferred embodiment of the present invention, the trial body portion is provided with 90.degree. guide surfaces for either purposes of checking the accuracy of the right angle cut or to be utilized as a saw blade guide surface. In the preferred surgical method, the surgeon first prepares the proximal femur, making the 90.degree. cut in a rough fashion and takes the trial proximal body and completely checks the accuracy of his right angle proximal cut. The surgeon may also use the trial body guide surfaces as a saw guide. Since the stem is not attached to the trial body portion at this time, the surgeon can easily check the accuracy of his cut. Having quickly and accurately created a bone bed for the proximal body portion, he can then move on to the distal trial stem portion and fit the stem to the femoral canal.
To accomplish this the surgeon will first insert various trial stem sizes to see which fits the patient best. If a stem fits well without any bone excavation in the femoral canal, he can quickly move ahead to the next phase of the operation. If he does need to prepare the femoral canal using rasps and/or reamers, he can quickly asses the stem fit and, if necessary, prepare the bone quickly because he can clearly see the stem within the femoral canal. This would not be possible with a one-piece trial because the integral head/body would obstruct his view.
Next, the surgeon attaches the trial stem chosen with the appropriate proximal body trial portion and places the assembled trial unit into position within the bone. At the time the surgeon implants an assembled two-piece trial, the fit has been determined and merely has to be checked. After checking, the surgeon seats the corresponding sized implant into the femur.
Because the surgeon has available a predetermined number of prostheses having different body and stem sizes, some of which overlap, it is imperative that the trial body portion and the trial stem portion chosen for the sizing operation correspond to a femoral component size available. In a preferred two-piece trial component system of the present invention, each piece has a male and female element for coupling the two pieces together which includes a key mechanism that, if the combination stem and body produces an available prosthesis size, mates, but if there is no available prosthesis size, does not mate. Consequently, the surgeon knows at the time of trial that he will not be able to find a femoral prosthetic component for implantation matching the trial component.